Means for controlling edging machines



Sept. 29, 1953 c. A. ELLIS MEANS FOR CONTROLLING EDGING MACHINES 2 Sheets-Sheet 1 Filed NOV. 15. 1947 INVENTOR. CHARLES A. ELLIS ATTORNEY Sept. 29, 1953 c. A. ELLIS MEANS FOR CONTROLLING EDGING MACHINES Filed Nov. 13. 1947 2 Sheets-Sheet 2 INVEN TOR.

CHARLES A. ELLlS ATTORNEY Patented Sept. 29,1953

UNITED STATES PATENT OFFICE Application November 13, 1947, Serial No. 785,590

This invention relates to new and improved means for forming and controlling the contour shapes of articles and relates more particularly to electronic means for controlling the operation of edge grinding machines used for this purpose.

It has been the general practice in the past when forming the contour edges of articles such as ophthalmic lenses to use a pattern or former, whereby a lens blank located in a grinding machine adjacent the grinding wheel will be rotated in a head so that the contour edge of the lens upon completion'of the grinding operation will be shaped in conformity with the contour edge of the former. Many different types of means have been employed to control the operation of grinding machines to produce the best results. However, past attempts have generally terminated in slight improvements in final results gained at the expense of sacrificing other desired features. To illustrate this, in using prior art type electrical'means for controlling the operation of the grinding mechanism, the additional speed gained by such a control method is more than offset by the shorter life of the machine and continuous servicing made necessary by the burning of the electrical contacts due to the high current necessary to properly operate the device, and an additional very undesirable feature is the danger to the machine operator always presented by parts of the machine carrying high voltage.

Therefore, it is one of the principal objects of this invention to provide electronic means for controlling the operation of machines of the above character, which means will overcome all of the difficulties of the prior art and, in addition thereto, will introduce many new and novel features.

Another object of the invention is the provision of improved means for controlling the operation of edge grinding machines to employ the principle of plunge grinding to considerably shorten the time required for the operation.

Another object is the provision of an improved device for forming the contour edge of an article such as an ophthalmic lens satisfactorily in substantially one complete revolution. I

Another object is the provision of an edge grinding machine having visual means for indicating the operative condition of the means for controlling the rotation of the article being ground.

Another object is the provision of electronic control apparatus for edge grinders having time delay safety means associated therewith to insure longer life of the electronic control apparatus.

control means for edge grinders adapted to automatically advance the article'to be formed only as fast as the article is ground to desired size and ape. J a

Another object is the provision of electronic Another object is the provision of electronic 3 Claims. (01. 51-101) control means adapted to be easily attached as a unit to existing edge grinding machines of the character set forth.

Further objects of the invention are to provide, as hereinafter set forth, an electronic control device for edge grinding machines which is simple in its construction and arrangement, durable, thoroughly efiicient in its use, readily attachable, and comparatively economical to manufacture.

Other objects and advantages of the invention will become apparent from the following description taken in connection with the accompanying drawings in which:

Fig. 1 is a perspective view of an edge grinding machine with an electronic control device attached thereto;

Fig. 2 is a fragmentary side elevation of the mechanism disclosed in Fig. 1;

Fig. 3 is a fragmentary side elevation of the circuit making and breaking means controlled by the pattern attached to the grinding machine;

Fig. 4 is a fragmentary plan view of the disclosure illustrated in Fig. 3; and

Fig. 5 is a schematic wiring diagram of the circuit showing diagrammatically the electronic control for associated parts of the edge grind- 1 ing machine.

rotating an article to be edged such as an ophthalmic lens, the lens is generally rotated at a constant speed throughout the entire edging operation and it is well known that under these circumstances some portions of the periphery of the lens being edged will become shaped to the proper size before other portions due to the fact that most lenses being shaped will be of uneven contour, thereby requiring more material to be removed in some portions than in others. Also, hard spots may be encountered in certain portions of the glass which will require more time for grinding these portions. Thus it will be seen that if the lens is rotated at a constant speed throughout the edging operation, considerable time may be lost while the portions of the lens requiring less grinding must be slowly rotated to bring other unground portions into position for grindmg.

Although many attempts in the past have been made to provide efficient means and methods for intermittently rotating the article to be edged, these devices have not been entirely satisfactory. Varioustypes of mechanical and hydraulic controls have been devised for this purpose but they have generally proved to be slow and inefiicient and, therefore, not practical for modern high-speed production methods. Electrically controlled devices for this purpose have been the nearest approach to the desired control mechanism but have had some undesirable features, among them being the necessary expense I and loss of time involved in repair of parts such as electrical contacts which, due to the high cur-.

rent passing through them, usually become Also, there may exist in some controls off this type constant arcing between the contacts located on or in connection with some of the moving machine parts. This arcing also will cause the contacts. to. become pitted or burned because of the high voltage passing between the contacts. These conditions are very undesirable especially when occurring in the manufacture of such articles as ophthalmic lenses since'the lenses may be finally formed inaccurately as to desired finished sizes, and shapes and the texture of the edge surfaces impractical for use. In addition, many times the parts of electrically controlled machines carrying high voltage are disposed in such, positions that they may be accidentally contacted by the machine operator.

The present invention is adapted to overcome these. and other difiiculties found in prior art machines by electronically controlling the intermittent rotation of the article relative to the grinding wheel in accordance with the amount of material to be removed from the portion of the article in direct engagement with the grinding wheel. Such electronic control, as hereinafter disclosed, has proved to be not only faster but much more positive in action with no breakdown caused by arcing and burning of the contacts andthe like and is comparatively simple in its construction and entirely automatic in its operation.

In the present device, electronic means are used to control the intermittent rotation of the article to be abraded wherein high resistance low current circuits substantialyfree from inductive effects are used to control the operation of the abrading machine. Also, with the present device, it is possible to use the principleof the plunge cut whereby in forming the contour shape'of the article being abraded, the first as wellas each of the succeeding cuts or grinding operations may be made to. the finished dimension, thereby requiring only a single complete revolution of the article to complete the contour thereof to its final size and shape. In addition, there is also provided the novel feature of signaling means whereby the machine operator will receive visual indication informing him when the device is being operated to rotate the lens, the signaling means also indicating the completion of the revolution of the article and consequently the completion of the edging operation.

Another very desirable feature is the incorporation in the present invention of a time delay type of safety means to prevent possible failure of the electronic device used to control the rotation of the article being abraded, thereby lessening the possibility of breakdowns within the electronic control.

Such an'electro'nic control-device as presented by the following description and shown in the accompanying drawings may be attachable as separable units to abrading machines already made and in use or they may be builtinto the machinesyvhei'i the. machines are being con structed."

versi'ng the "pulley; the belt being connected to 4 Referring more. particularly to the. drawings wherein like characters of reference designate like parts throughout the several views, the device embodying the invention as illustrated in Fig. 1 comprises. broadly an edge grinding machine l0 having a base H on which a grinding stone or wheel [2: isrotatably supported in bearings H by means ofja'rbor l4.

Bower istmmmtted to the arbor i4 through a pulley l5 mounted thereon and a belt l6 transany suitable constant source of power not shown.

A drive shaft I!) in the ordinary edge grinding machine is operatively comiectedat itsforward end to gear and worm mechanism located within a gear box 20, which mechanism operates in response to therotarymovement. of shaft. 19: to rotate a horizontal shaft journaled in the. head 2| and about which the said head swings. and whichin turn operates through additional gearing to synchronously rotate gears. 22 and 23. A pair of longitudinally spaced head and tail spindles 2d. and 25.. are journaled in the upper portion of the head 2|, spindle 24 carrying at its outer end gear 22', with gear 23 being fixedly mounted about. midway on spindle 25. The inner adjacent ends of the spindles. 24 and 25 are provided with pads 26. between which is carried the article 21 which is to be shaped. The article may be formed of glass, metal or any. other desired material which is to be provided with a shape controlled by a pattern or former. It may be a blank for a pattern, a watch crystal, lens blank or other similar article but for ease of description it is referred to throughout as being a lens blank. A handle 28 located on the front of the head 2| may be manually operated to spread the spindles 24 and 25 to release the lens blank as well as todraw the inner ends of the spindles toward one another to clamp the blank in position through means commonly known in the art. The lens blank 21 when in place between the pads 26- on the ends of spindles 24 and 25, will thus be rotated continuously through the mechanism described above, with the edge of the blank being in abutting relation with the abrading surface of the grinding wheel H which through its rotation will tend to remove material from the abutting contour edge of the blank.

The head 2| is pivotally attached to the base I as set forth above and may be swung toward or away from the grinding wheel |2.. It is normally urged toward the grinding wheel by a weight 91. The movement of the head 2| and consequently the lens. blank 21 relative to. the abrading surface of the grinding wheel !2 is controlled by a pattern or former 29 which is at taohed to the outer end of spindle 25 by any suitable means. Thepattern 29 is of the shape of the lens to be ground. Upon operation of the gear mechanism the pattern, in being rotated against a contact shoe 32 having. a suitablehard, rigid surface, will cause the head 2| to swing forwardly or rearwardly in accordance. with the irregularities in the contour of the pattern. It will be seen that in a device of the character wherein the pattern and the blank are continuously rotated at a predetermined speed the high spots of theblank will require more rotations of the blank in grinding them off than will the low spots. Therefore, the time when the finished low spotsv rotate past the area adjacent the grinding wheel to bring the high spots repeatedly into grinding position is entirely wasted.

seam" Several revolutions may be required before a high spot finally is ground to the finished dimension.

It is to be understood that the foregoing description is primarily based on a standard machine and hence forms no part of this invention except insofar as the drive mechanism for the grinding wheel is concerned with respect to its operation with related mechanism now to be set forth.

There is provided in the present construction electronic means for controlling the rotation of the blank to permit the contour edge of the blank tobe reduced substantially to size in a single cycle of movement. With reference to Figs. 1 and 2, the rotatable drive shaft I9 .has its central portion cut away which, in attaching one of these electronic controls to a standard machine, will leave one portion 30 of the shaft i9 unused and merely projecting slightly from the gear box It depending upon the length of the portion eliminated. The opposite forward portion 3| of the shaft l9 projects rearwardly from the gear box 213 and is connected by a coupling 32 to a motor drive shaft 33 operated by a motor 34, the motor being mounted by suitable means upon the machine base ll and operatively controlled by electronic means enclosed within a housing 35 secured in some advantageous position on the machine whereby the said electronic means will also function as a signaling device and will be readily visible to the machine operator within the housing 35 through the opening 3%.

In the present illustration the housing 35 containing the electronic control means is shown secured to the top of the safety guard 31 of the grinding wheel E2 and thereby within the direct vision of the operator.

It can readily be understood that, with this construction, operation of the motor 34 will cause rotation of coupling 32 and forward portion 3! of the shaft 29 to rotate the lens blank 21 and pattern 29 through means recited hereinbefore, and that when the operation of the motor Mis discontinued this will consequently stop rotation of the lens blank 2'! and pattern 29 and allow that portion of the lens blank held in engagement with the abrading surface of the grinding wheel E2 by the weight if to be ground at said abutting area. The extent of said grinding is controlled by the engaging of the pattern 29 with the contact shoe 42.

A laterally disposed shoe supporting member 33 is fixedly mounted on the machine base i I below the pattern supporting end of shaft 25 and above gear box 2%} and carries at its rearward end an upwardly extending adjustable bracket 3s. The bracket 39 is shaped to present a forwardly projecting vertical surface spaced slightly above the supporting member 38 having a longitudinal groove therein adapted to carry the rear edge of an insulating member 48 firmly located therein by means of pins 4| or the like.

Thecontact shoe 32 is mounted over the forward edge of the insulating member 49 and held immovably in position by a press fit connection. As

and which indicated in the drawings by refer-- will initially cause a suitable source of power to be directed to the grinding machine to impart rotation of the grinding wheel i2 through belt l6, pulley l51and arbor l4, causing the grinding wheel to revolve continuously until said source of power is rendered inoperative by the machine operator.

A lens former or pattern 29 of the desired shape of the finished lens to be ground is then mounted on the outer end of tail spindle 25 which is journaled in the head 2 I the head during these initial setting up operations being stationary and swung and held in a position away from the grinding wheel 12. At this point the handle 28 may be manipulated by the operator to open the space between the pads 26 on the ends of the head and tail spindles 2t and 25 for insertion of a lens blank 27 to be ground between said lens supporting pads 26, the handle 28 being returned to its initial position to close the space between the pads and to clamp the lens blank firmly in position in the conventional manner.

ward and away from the grinding wheel l2. Al-

though it normally is inoperatively positioned? in a substantially vertical position, in operation it is constantly urged toward the grinding wheel by the weight I! mentioned above and will position and hold the contour edge of the lens blank 2'! against the abrading surface of the revolving grinding wheel. Other suitable means may, if desired, be incorporated to provide additional adjustments with respect to the pressure required to maintain the head in position so that the lens blank will constantly engage the wheel. The resultant size of lens is controlled by the initial adjstment of the contact shoe 42 inwardly or outwardly relative to the abrading surface of the. grinding wheel through suitable adjusting mechanism housed in the supporting member 38 and operated by the thumb wheel 50 in the conventional manner.

In the actual lens grinding operation, the lens blank 27, which has been fabricated as to the optical surfacesformed thereon as prescribed by an optician, is allowed to rest in edge contact against the abrading surface of the .grinding wheel under the action of the weight I! described above. 'When the lens blank 21 first engages the wheel 12 the former or pattern 29, because of the initial size of the blank, will be held spaced from the shoe 42. Howeven'as the edge of the lens is ground by the revolving grinding wheel the pattern 29 will approach closer to shoe 42 until'it finally actually makes contact with the shoe to prevent the head from swinging further toward the grinding wheeland thus preventing can be seen .by referenceto Figs. 3 and 4, the edge of thepattern or former 29 is adapted to engage the shoe 52 to control the'operation of the invention as. will be made clear in the description of the operation of the machine which follows.

Mounted within the housing 35 is the electronic means for controlling the rotation'of the lens blankand which includes a thermionic tube conadditional material from being ground off the edge of the lens blank at said location. This completes the initial cut or what is known as a plungecut; that is, the lens edge at said location has been reduced toits finaldepth in one cut.

The contacting of the pattern 29 with the shoe 1&2 at thejcompletion of the initial plunge cut causes the motor 34 to be energized and thereby causes the lens blank to be rotated an amount sufficient to present anadjacent uncut portion ofthe blank to-be' abraded ina similar manner. I taming mercury vapor, argon or othernoble gas, When the progressive adjacent uncut portion of en ages e ens ank. i a van dr h ou h hei nera zing of the motor the rotation thereof,w i1lsirnul-.- taneously cause thepattern to .b ecom,e disengaged m h nt ct hqea d. llautoma itally eenergize the motor whereupon thelens, blank will a n. o ary fo are iodoi time.,suhicient. to allow theabrading. wheeLto grind th newlyv presented portion of the blank to a depthwherein the patternwill again contact theshoetocausea;

repetitive function to. takfihlaoe These llqcessive plunge cuts are formed intermittently throughout. the entire contour, of the lens blank and will there y reduc the lahkto he hape or. the pattern.

The ne gizing nd, .de-.- iere. zih ,0 the. motor. s lt rom the'nrq sion. oi. an. e ectr cal. system embodying an. electronqtubeg'flgofi the...

thermionic type, Thistubeembodiesa filament.

,.a an and.an1ate 4;an,d.has itsinte ior fil ed th a. gas. suc mercury vapor, argon o Q her. obla a as p evious y. tated. This. ec nt be uhct hs n pen and los t i ult. the mete a di ts op rat on iscontrolledby a re at v y. 10W o ta e. a ompared. with th l a e. quirediorcnnehing t e motor 3 The p ary oil 'Q ia trans ormer is. con.- e ted th ough ircuit; l t h incomin r eoi.e eqtricalihergy hese ond r coil of.- the transformer being. connect dithrough circuit d. t th filament. 'tq sa d lectrcntub 3,- he. ircuit al i mhq ie a imed iar r lay tub fi vinsaheat rii it;5!i he einan m ke-anm break contacts 493;; The heating unit}! is conect dhrthe lead et heconductpr c andi y the. adj otha cmiu tcr. d n p ral el with the.

lamht; Qfith ectron tutti; One oix he n c s. fi s.. hnecteci' y. hec nd n a t QeAZithr AQh-thQ en inal The. he 'O a i. h aqts-A Biis hn c edmy the l ad re 1? t a res stprcir iiit on r liingtheopera nime,e idiiinthe el ct cn be 43;; These. resistors are indicated by B, I 32;; 12.3;134", R5 and 61. In this. instanc he ead-r. socnnectedi irectly hthe.re istorhl'w ch nturn s nne d: quehthaleadm. o. h idifl. of. the.

tron ube.

The'contacts 49"ofthe delay relaytube4fi are normally in open relation and are in series .with

uctor to the:

theflcontrol-circuitto-the shoe 42-an lipattern,29.

Heating of the delay -tu be heater 51- closes the contacts waiter a given time intervalsuch as, for; example, forty seconds., During this interval; the

filament of the electron tube 43" has had ample time to reach its operating temperature. i This-is,

necessary only when first starting, the machineg caused-by not waitingasufiicient intervahfor the,

so at. the er t r llnot en o nte fiicul ie t n t e. t hecQ iepm erly. heated. The

p t Qf. the.,.el c. rpn .Itube ..43 connected.-

throughthe conductor a directly to one sideoi is connected through theconductors.hb-.to,one

Side of the alternatin c rr nt suppl 3 The other side .a, of the; alternating. current supply is: conducrtively. connected .to the ,tube filament through \A-c and/or (1, the electron streamebetweenthe:filai ment and; plate; completing; the-. motor circuit;

under operative conditions.

e r 21 fith elesztrcm uba 8:.is 0rmal1y egat v nd: negatire olta e-is upplied; by:

ia i uit. ncl ding. a al swava re. t .fier.- B,;-.

locatedin the Ecirc t on the leadqmbetween con-.1

ductor band .a'pair.oidroppingfresistq s ka d Bathe r ctifier: 48. s rif-inertia;c n ert-the; alt .r

nailing current,-,Sl DP, idrby, 1 6331%.(1712; to direct;

the motor 34 and the opposite side ofsaid motorcurrent... Thus, negative or minus voltage issup-'- plied from the rectifier 48' and resistorsRB: and

R6 through conductor r, resistors R2 andRl. and conductor m to the grid 52. desired tolconduct true direct current to the grid. rather than pulsating. current as supplied by thev half -.wave rectifier 48;, a condenser C2 is inserted betweenresistors R5 and R6, the condenser acting,-

to store energy in this circuit and. to discharge energy between the waves dischargedby the halfwave rectifier 48, thus, providing essentially-direct, current through. resistor R5. and onto the grid 52. The resistor BI. is insertedin the circuit for. protection of the grid to limit current flowing to the grid.

Resistors R4, R3 anclRS are inser'iesandprovide an alternating. current network, circuitv be-R4R3r- -R,5--ga, the values of the. resistors being selected so that voltage acrossRi isnot enoughto allow. conductor 1 tobe positive. with respect to the filament 53' of the electrontube. However, upon contact being made between the pattern 29 and shoe 42 resistors R2 and R3, are-placed in parallel. as shown in Fig. 5 by lead line n connected at 44 to shoe 42 andthrough contacts 49 andlead linep. Lead line k has oneend connected at 45 tothemachine and thus-the circuit is completed through the machine to the pattern 29. The opposed end of said lead line It is connected between resistors R3 andR4. tween the shoe 42 and former 29-the resistance of the R3-R4R5 circuit is reduced toa pointwhere the voltage across resistor R5 willrise'to such a degree as to permit positive pulsesto be supplied to the grid 52v of the electron tube 43,

through conductor r, resistors R2 andv RI and:

this will start the flow of electrons-to-the plate,-

54..which also -is positive and thence through conductor 7' to themotor 34. Thus, the-motor is supplied with pulsating currentthrough circuits ac or a--d to the tube 43 and lead a,

thence through conductors h and=b to complete the circuit thereto.

A condenser Cl is connected in parallel withthe motor, leads b and y, to improve the operation of the motor by furnishing impulsesduring the time the electron tube is non-conductive.

This is accomplished by'the condenser becom' ing charged during the conducting cycle of the tubea-nd'by its discharging'through the motor in the non-conducting cycle.

Resistor R'Hn series/with the condenser Ci is-provided fir the purposeof-limiting the peak of inrush current to the condenser-to reducethepossibilityof its failure;-

Immediately upon being. energized, the motor blank into abrading position as described above. Thislwill cause the head2 I to swing in a direction away from the grinding wheel [2 thus. causing the pattern; 29, to become disengaged from the contact shoe-42; thereby breaking the circuitto the -r esistornetwork, converting the voltage 'to theg-rid:5,2,of'e1ectrontube 43 to negative polarity.

Due:to;the;characteristic;of this-electron tubeythisi.

However, sinceit This circuit iseffected When contact is madebe- 34will.operate torotate the lens blank 2] and" pattern 29. to bring an uncutportion of. the lens electrons from filamentj53 to the plate 54 as soon as the plate Voltage passes through zero to thus breakthe circuit to the motor 3 de-energizing the motor and stopping the rotation of the lens blank and pattern.

The motor will not operate to rotate the lens blank again until the portion of the blank in abutting relation with the grinding wheel l2 has been cut to the depth desired as controlled by the pattern 29, at which time the pattern will again make contact with the shoe 42 to again energize the motor 34 as described and the cycle is repeated until the entire contour edge of the lens blank has been ground to the size and shape of the pattern, after which it maybe removed from the machine and a new lens blank to be ground may be substituted in'its place.

It is important here to note that the electron tube 43 is mounted within the control housing 35 in such a position that it can be visible through the opening 35. The gas within the tube'is of such a type that it will become luminous when current is passing between the filament and the plate of the tube, thereby indicating visually to the operator when the motor is being energized to rotate the lens blank. It is also important to note that the blank is rotated by the motor 35 only a very small amount since the contact between the pattern andshoe is almost immediately broken. Only a small amount of material is removed from the blank during each grinding operation or between each interval of contact of the blank with the grinding wheel and the interval of contact of the pattern 29 with the shoe 42. That is, the lens is ground during the period that contact is broken between the pattern 29 and shoe G2 and until contact is again established between these members. Therefore, there will be numerous engagements and disengagements between the shoe and the pattern in grinding each edge surface of the lens blank, or such surfaces as correspond to the surfaces of the pattern 29. The entire edge surface is not removed at each engagement between the lens blank and the grinding wheel, but instead only a small portion, or so much of the blank as can be presented to the abrading surface of the grinding wheel. As a result there will be numerous engagements between the pattern and shoe for intermittently rotating the'lens blank, because the lens blank will be out of pressure contact with the wheel when the pattern 29 engages the shoe 42.

One complete turn or revolution of the lens blank is suflicient generally to remove the necessary material to bring the blank down to proper size and shape. However, as the last amount of material is removed, the pattern and shoe will again make contact and the circuit to the motor 34 will be established to permit the lens blank to, again be rotated. This second rotation of the lens blank, if desired, will be made at a high rate of speed and, together with the rotation of the grinding wheel, insures the removal of any superfiuous material and cleans up the tiny scallops onthe edge of the blank. One revolution of the blank under this condition is sufficient to perform this cleaning up operation although the blanks are satisfactory for general use without the added operation. The continuous rotating of the lens blank and therefore the continuous i1- lumination of the tube indicates to the operator that the lens is completed.

With this method of removing the material 10 and'the forming of a lens, production time is reduced considerably compared with the general methods employed for this purpose, together with the added advantage of greater safety provided through the use of a high resistance circuit in areas most likely to be contacted by the operator.

It can be clearly seen from the foregoing that an abrading machine of the character described hereinbefore is an improvement over prior art machines by providing efficient and simple electronic control for operation thereof, said electronic control including the employment of the principle of plunge grinding which considerably shortens the time required for a grinding operation of an article to shape the contour edge of the article satisfactorily in most cases in one complete revolution of the article, with a second revolution of the article being made if desired, the electronic control for the machine also having visual means for indicating the operative condition thereof and safety means associated therewith to insure longer life of the apparatus, in contrast to the short life of prior art devices. Electronic controls for abrading machines of the character described may be easily attached as units to existing edge grinding machines of the character set forth.

It will be apparent that many changes may be made in the details of construction and arrangement of parts shown and described without departing from the spirit of the invention as expressed in the accompanying claims. Therefore, it is to be understood that all matter set forth or shown in the accompanying drawing is to be interpreted as illustrative and not in a limiting sense.

I claim:

1. A lens edging machine of the character described comprising a rotatable abrading wheel, a rotatable work holding device for supporting a lens in position 'to be edged by said abrading wheel, said'work holding device being supported for movement in a controlled path toward and away from said abrading wheel, a pattern rotatable with said work holding device, a contact positioned to be engaged by said pattern to control the relative spacing of said work holding device to the abrading wheel, electrically operated drive means imparting simultaneous rotary movement to the work holding device and pattern when electrically energized, a circuit for connecting said drive means to an A. C. source, a three element type gas-filled electron tube embodying a cathode, plate and intermediately disposed control grid and having its cathode and plate connected in said'circuit on one side of the drive means whereby there will be an A. C. potential on the plate when the drive means is connected by said circuit to an A. C. source, and a pair of bias circuits of fixed potential connected with said grid, one introducing D. C. voltage of negative polarity on the grid and the other simultaneously introducing voltage of positive polarity on said grid, said tube firing only when the grid is positive with respect to the cathode, and the bias circuit of negative polarity normally having a value slightly in excess of that of the positive polarity bias circuit to prevent firing of the tube, and means operable by engagement of the pattern and contact for increasing the potential of said positive polarity bias circuit to a value where it exceeds that of the bias of negative polarity to permit the tube to fire and allow the circuit to energize the drive means to rotate the work holding device and advance an adjacent unabraded portion of the lens to a position where the pattern and contact will disengage and cause the bias circuit of negative polarity to again become of greater potential so as to substantially instantaneously stop the said advance of the lens when the potential of the A. C. on the plate goes to zero and allow said portion of the lens edge to be ground, whereby in one complete revolution of the lens it may be edged to substantially the exact shape of the pattern.

2. A lens edging machine of the character described comprising a rotatable abrading wheel, a rotatable work holding device for supporting a lens in position to be edged by said abrading Wheel, said work holding device being supported for movement in a controlled path toward and away from said abrading wheel, a pattern rotatable with said work holding device, a contact positioned to be engaged by said pattern to control the relative spacing of said work holding device to the brading wheel, electrically operated drive means imparting simultaneous rotary movement to the work holding device and pattern when electrically energized, a circuit for connecting said drive means to an A. C. source, a three element type gas-filled electron tube embodying a cathode, plate and intermediately disposed control grid, said tube having its cathode and plate connected in said circuit on one side of the drive means whereby there will be an A. C. potential on the plate when said circuit is connected to the A. C. source and said tube firing only when the grid is positive with respect to the cathode, and a pair of bias circuits connected with said control grid, each bias circuit including a plurality of resistors in series controlling the value of its potential, at least one of which resistors is common to both circuits and said circuits each further having at least one resistor separate from the other circuit, one of said bias circuits introducing voltage of positive polarity on the grid of predetermined normal value and the other bias circuit introducing D. C. voltage of negative polarity on the grid and having the value of its resistors such as to introduce negative voltage of a potential just over the normal value of the positive voltage of the first bias circuit to prevent firing of the tube, a make and break circuit connecting in parallel relation a resistor common to the two bias circuits and a resistor only in said positive polarity bias circuit, said latter circuit being completed by engagement of the pattern and contact to change the relation of the resistors in said positive polarity bias circuit from their normal series to said parallel relation to increase the potential of said circuit to a value where it exceeds the potential of the negative polarity bias circuit to permit the tube to fire and allow the circuit to energize the drive means to rotate the work holding device and advance an adjacent unabraded portion of the lens to a position where the pattern and contact will disengage to break said further circuit and cause the potential of the negative polarity bias circuit to again be of greater potential so as to substantially instantaneously stop the said advance of the lens when the potential of the A. C. on the plate goes to zero and allow said portion or the lens edge to be ground, whereby in one complete revolution of the lens it may be edged to substantially the exact shape of the pattern.

3. A lens edging machine of the character described comprising a rotatable abrading wheel, a rotatable work holding device for supporting a 12 lens in position to be edged by said abrading wheel, said work holding device being supported for movement in a controlled path toward and away from said abrading wheel, a pattern rotatable with said work holding device, a contact positioned to be engaged by said pattern to control the relative spacing of said work holding device to the abrading wheel, electrically 0perated drive means imparting simultaneous rotary movement to the work holding device and pattern when electrically energized, a circuit for connecting said drive means to an A. C. source, a three element type gas-filled electron tube embodying a cathode, plate and intermediately disposed control grid and having its cathode and plate connected in said circuit on one side of the drive means whereby there will be an A. C. potential on the plate when the circuit is connected to the A. C. source, said tube firing only when the grid is positive with respect to the cathode, and a pair or series resistor bank bias circuits connected with its grid, each circuit having at least one resistor common to the two circuits and a resistor separate therefrom, said bias circuits being connectable to the A. C. source, one bias circuit introducing alternating positive and negative pulses of voltage on the grid of a value determined by the resistors in its circuit, and the other bias circuit including a rectifier and having the values of its resistors such as to introduce negative D. C. voltage of a potential just over the normal value of the positive pulse of the first bias circuit to prevent firing of the tube, a make and break circuit connecting in parallel a resistor common to the two bias circuits and a resistor only in said positive potential introducing bias circuit, said latter circuit being completed by engagement of the pattern and contact to change the relation of said resistors from series to parallel relation to increase the potential of said circuit to a value where it exceeds the potential of the negative polarity bias circuit to permit the tube to fire and allow the circuit to energize the drive means to rotate the work holding device and advance an adjacent unabraded portion of the lens to a position where the pattern and contact will disengage and cause the bias circuit of negative polarity to be of greater potential so as to substantially instantaneously stop the said advance of the lens when the potential of the A. C. on the plate goes to zero and allow said portion of the lens edge to be ground whereby in one complete revolution the lens may be edged to substantially the exact shape of the pattern.

CHARLES A. ELLIS.

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